The average rate of hair fibre growth is around 0.35mm a day but this rate varies depending on the site of the hair follicle and the age and sex of the individual.
The duration of the anagen growth phase for scalp hair is usually 6-10 years while telogen lasts just 30-90 days and catagen is best estimated at 14-21 days.
Normally this cycle of hair production and inactivity will continue for the duration of the individual's life but other factors can influence and inhibit hair production. Factors may include adverse reactions to drugs and cosmetics, or as a result of scarring, tumors, radiation, the genetics of the individual, hormones and/or their immune system.